Electroless nickel coatings and compositions and methods for forming the coatings

Abstract

An aqueous electroless nickel plating bath for forming electroless nickel coatings includes nickel, a hypophosphorous reducing agent, zinc, a bismuth stabilizer, and at least one of a complexing agent, a chelating agent, or a pH buffer, and is free of a sulfur compound.

1 . An aqueous electroless nickel plating bath for forming a black electroless nickel coating, the bath comprising:
 nickel,   a hypophosphorous reducing agent,   zinc,   a bismuth stabilizer, and   at least one of a complexing agent, a chelating agent, or a pH buffer, and   wherein the bath is free of a sulfur compound.   
     
     
         2 . The bath of  claim 1 , wherein hypophosphorous reducing agent is selected from the group consisting of sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, and combinations thereof. 
     
     
         3 . The bath of  claim 1 , wherein the at least one pH buffer, complexing agent, or chelating agent is selected from the group consisting of acetic acid, formic acid, succinic acid, malonic acid, an ammonium salt, lactic acid, malic acid, citric acid, glycine, alanine, glycolic acid, lysine, aspartic acid, ethylene diamine tetraacetic acid (EDTA), and combinations thereof. 
     
     
         4 . (canceled) 
     
     
         5 . The bath of  claim 1 , wherein the nickel is provided in the solution in the form of a water soluble nickel salt. 
     
     
         6 . The bath of  claim 5 , the nickel salt being selected from the group consisting of nickel chloride, nickel bromide, nickel iodide, nickel acetate, nickel malate, and nickel hypophosphite. 
     
     
         7 . (canceled) 
     
     
         8 . The bath of  claim 1 , having a pH of about 4.5 to about 5.0. 
     
     
         9 . The bath of  claim 1 , comprising about 2 g/l to about 10 g/l nickel, about 20 g/l to about 35 g/l of the hypophosphorous reducing agent, about 1 g/l to about 75 g/l each of the complexing agent, chelating agent, and/or pH buffer, about 40 ppm to about 120 ppm zinc, and about 5 ppm to about 30 ppm of the bismuth stabilizer. 
     
     
         10 . The bath of  claim 9 , comprising lactic acid, acetic acid, malic acid, succinic acid, sodium hypophosphite, ammonium hydroxide, nickel, zinc, and ethylenediamine tetraacetic acid. 
     
     
         11 . A method of forming a black electroless nickel coating on a substrate, the method comprising:
 contacting a surface of the substrate to be coated with an aqueous electroless nickel plating bath, the bath including nickel, a hypophosphorous reducing agent, zinc, at least one of a complexing agent, chelating agent, and/or pH buffer, and a bismuth stabilizer, wherein the bath is free of a sulfur compound;   etching the electroless nickel coating with an etchant agent to provide the coated substrate with a black surface.   
     
     
         12 . The method of  claim 11 , wherein hypophosphorous reducing agent is selected from the group consisting of sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, and combinations thereof. 
     
     
         13 . The method of  claim 11 , wherein the bath includes at least one pH buffer, complexing agent, or chelating agent is selected from the group consisting of acetic acid, formic acid, succinic acid, malonic acid, an ammonium salt, lactic acid, malic acid, citric acid, glycine, alanine, glycolic acid, lysine, aspartic acid, ethylene diamine tetraacetic acid (EDTA), and combinations thereof. 
     
     
         14 . The method of  claim 13 , comprising at least two of a pH buffer, complexing agent, and/or chelating agent. 
     
     
         15 . The method of  claim 11 , wherein the nickel is provided in the bath in the form of a water soluble nickel salt. 
     
     
         16 . The method of  claim 15 , the nickel salt being selected from the group consisting of nickel chloride, nickel bromide, nickel iodide, nickel acetate, nickel malate, and nickel hypophosphite. 
     
     
         17 . (canceled) 
     
     
         18 . The method of  claim 11 , wherein the pH of the electroless nickel plating bath is maintained at about 4.5 to about 5.0 and the temperature about 175° F. to about 200° F. 
     
     
         19 . The method of  claim 11 , the bath comprising about 2 g/l to about 10 g/l nickel, about 20 g/l to about 35 g/l of the hypophosphorous reducing agent, about 1 g/l to about 75 g/l each of the complexing agent, chelating agent, and/or pH buffer, about 40 ppm to about 120 ppm zinc, and about 5 ppm to about 30 ppm of the bismuth stabilizer. 
     
     
         20 . The method of  claim 11 , the bath comprising lactic acid, acetic acid, malic acid, succinic acid, sodium hypophosphite, ammonium hydroxide, nickel, zinc, and ethylenediamine tetraacetic acid. 
     
     
         21 . The method of  claim 11 , the etchant agent comprising an iron blackening agent and an acid. 
     
     
         22 . The method of  claim 21 , the etchant agent comprising ferric sulfate and hydrochloric acid. 
     
     
         23 - 50 . (canceled) 
     
     
         51 . The method of  claim 11 , further comprising:
 contacting the substrate with a first electroless nickel plating bath to form a first electroless nickel coating on the substrate prior to contacting the surface of the substrate to be coated with the aqueous electroless nickel plating bath that is free of a sulfur compound, wherein the aqueous electroless nickel plating bath that is free of a sulfur compound forms a second electroless nickel coating over the first electroless nickel coating.   
     
     
         52 . The method of  claim 51 , the first electroless nickel coating having a phosphorous content about 7% to about 13% by weight. 
     
     
         53 . The method of  claim 52 , the second electroless nickel coating having a phosphorous content of about 8% to about 11%.